The effect of temperature on the nutritional requirement of microorganisms.

Recently we reported the microbiological determination of L-phenylalanine and Land n-phenyllactic acid with Lactobacdlus arabinosus as the test organism (1). Although phenylalanine is not an absolute dietary essential to this organism, a microbiological determination of the amino acid is possible, for, in the absence of the amino acid or its metabolic derivatives, there is no visible growth at 35” until after 40 hours have elapsed. However, in the course of studies on the synthesis of this amino acid by L. arabinosus it has been found that below 35” the organisms grow rapidly without phenylalanine, but at 37” they did not grow at all, even during incubation periods of 72 hours or longer. The profound effect of small changes in temperature on the synthetic ability of the organism was traced to associated changes in carbon dioxide tension. Studies on the effect of temperature on microbial synthesis have been extended to other amino acids, and in this report findings on tyrosine, aspartic acid, and histidine, in addition to phenylalanine, are presented.